Important: qemu-kvm-rhev security and bug fix update

Details

Updated qemu-kvm-rhev packages that fix one security issue and two bugs arenow available for Red Hat Enterprise Linux 6.

The Red Hat Security Response Team has rated this update as havingimportant security impact. A Common Vulnerability Scoring System (CVSS)base score, which gives a detailed severity rating, is available from theCVE link in the References section.

KVM (Kernel-based Virtual Machine) is a full virtualization solution forLinux on AMD64 and Intel 64 systems. The qemu-kvm-rhev packages form theuser-space component for running virtual machines using KVM.

A flaw was found in the way QEMU handled VT100 terminal escape sequenceswhen emulating certain character devices. A guest user with privileges towrite to a character device that is emulated on the host using a virtualconsole back-end could use this flaw to crash the qemu-kvm process on thehost or, possibly, escalate their privileges on the host. (CVE-2012-3515)

* This flaw did not affect the default use of KVM. Affected configurationswere:

- When guests were started from the command line ("/usr/libexec/qemu-kvm")without the "-nodefaults" option, and also without specifying aserial or parallel device, or a virtio-console device, that specificallydoes not use a virtual console (vc) back-end. (Note that Red Hat does notsupport invoking "qemu-kvm" from the command line without "-nodefaults" onRed Hat Enterprise Linux 6.)

- Guests that were managed via libvirt, such as when using Virtual MachineManager (virt-manager), but that have a serial or parallel device, or avirtio-console device, that uses a virtual console back-end. By default,guests managed via libvirt will not use a virtual console back-end for suchdevices.

* This flaw did not affect the default use of a Red Hat EnterpriseVirtualization host: it is not possible to add a device that uses a virtualconsole back-end via Red Hat Enterprise Virtualization Manager.

To specify a virtual console back-end for a device and therefore bevulnerable to this issue, the device would have to be created another way,for example, by using a VDSM hook.

Red Hat would like to thank the Xen project for reporting this issue.

This update also fixes the following bugs:

* Previously, the KVM modules were not loaded by the postinstall scriptletof RPM scripts. This bug caused various issues and required the system tobe rebooted to resolve them. With this update, the modules are loadedproperly by the scriptlet and no unnecessary reboots are now required.(BZ#839897)

* Previously, when a guest was started up with two serial devices, qemu-kvmreturned an error message and terminated the boot because IRQ 4 for the ISAbus was being used by both devices. This update fixes the qemu-kvm code,which allows IRQ 4 to be used by more than one device on the ISA bus, andthe boot now succeeds in the described scenario. (BZ#840054)

All users of qemu-kvm-rhev are advised to upgrade to these updatedpackages, which fix these issues. After installing this update, shut downall running virtual machines. Once all virtual machines have shut down,start them again for this update to take effect.

Solution

Before applying this update, make sure all previously-released erratarelevant to your system have been applied.